Gordon Lightfoot did a whole lot of wonderful songs about the sea. One of them is about a blue whale, and would fit your requirements perfectly, I should think.

It's called "Ode to Big Blue" and appears on his 1972 album "Don Quixote". It's an excellent song.

"The oceans of the world were a home to Big Blue, He was the greatest monster that the world ever knew, and the waters to the west was the place that he loved best, around the blue Pacific he did roam..."

There's a bunch more verses...about whales, whaling ships, the fight for survival, and so on...can't remember them right now...find this song and learn it.

"Ghosts of Cape Horn" is another great Lightfoot song about the sea, but there are no see beasties in that one.